It is well known that amines such as hexamethylene diamine can be produced by the catalytic hydrogenation of nitriles such as adiponitrile in the presence of Raney catalysts.
One such process is described in U.S. Pat. No. 3,821,305, in which hydrogenation is conducted in liquid phase at pressures of from 20-50 atmospheres and temperatures of 60.degree.-100.degree. C. in the presence of finely divided Raney catalyst and an inorganic base. Hydrogen and adiponitrile are fed into a liquid reaction medium consisting of hexamethylenediamine, water, the inorganic base, and the catalyst, in which medium the content of base is maintained in the range of 0.2-12 moles per kilogram of catalyst, while the content of water is maintained in the range of 2-130 moles per mole of the base.
The process discharge stream in the above described process contains both Raney catalyst and the product hexamethylenediamine, from which it is desirable to recover substantially pure hexamethylenediamine by distillation, and to recycle the Raney catalyst.
During such separation procedures, the crude amine is exposed to the Raney nickel catalyst under conditions favoring its decomposition or dehydrogenation. This decomposition is substantial if the catalyst is not separated or passivated immediately after the process discharge exits the reactor. Even the small amount of catalyst that normally gets through most commercial processes for removing catalyst (centrifuge, decantation, filtration) result in significant decomposition of amine if the catalyst is not passivated.
The substantial elimination of such decomposition would constitute a significant improvement in the art and is an object of this invention.